1. Field of the Invention
This invention relates generally to a motor vehicle stabilizing apparatus. In particular, this invention relates to an apparatus for bringing an additional set of tires into contact with the road surface for use with a van or recreational type vehicle.
2. Background of the Invention
Many vehicles such as vans, campers and recreational vehicles possess an aerodynamically inefficient profile which presents a broad surface easily affected by cross winds. The shape of the vehicle is dictated by the designer's attempt to provide maximum internal capacity in a relatively compact shape. Such vehicles are generally in the shape of a rectangular solid, and possess a length substantially greater than their width. These vehicles are generally supported by a pair of axles, each axle containing one or two tires at each end. Vehicles of this type typically present a substantial surface area which is particularly susceptible to wind loading in a direction perpendicular to the direction of vehicle travel. Wind loading acting against the side of the vehicle can cause difficulty in maintaining the desired direction of travel and can cause the vehicle to sway or oscillate depending on the natural resonant frequencies of the vehicle structure.
In order to maintain stability in high winds, the configuration of many two axle vehicles dictates that each axle should be located at the extreme end of the vehicle. However, due to considerations of vehicle load carrying ability, weight distribution and a desire to reduce the vehicle's turning radius, the rear axle on such vehicles is typically located an appreciable distance inward from the rear end of the vehicle. The rear portion of a vehicle with such an axle configuration is thus cantilevered beyond the rear axle, up to as much as one half of the vehicle's entire length. Under high wind loading conditions, the rear portion of such a vehicle is unable to adequately resist the tendancy to sway or oscillate, thereby transmitting appreciable bending and torsional moments to the forward portion of the vehicle, making the vehicle difficult to control.
Motor vehicle designers have sought to increase the stability of generally rectangular, broad surfaced vehicles in numerous ways. One solution is to move the rear axle further towards the extreme rear end of the vehicle, but this modification increases structural loads on the center portion of the vehicle and has the undesirable effect of increasing the vehicle's turning radius. Another solution is to try to shape the side portions of the vehicle such that they present a less aerodynamically conspicuous configuration. Effective aerodynamic solutions, however, tend to reduce the internal capacity and utility of the vehicle. Finally, tire width may be increased in an effort to put a larger tread surface in contact with the road. This approach is only marginally successful because it adds stability to an area already anchored to the road surface and therefore does not address the problem caused by oscillation of the cantilevered portion of the vehicle.
Another person with large volume vehicles is the user's tendency to overload or improperly load the vehicle. Extremely heavy heads may be easily placed within a van or recreational vehicle with little consideration given to the limitations of the vehicle's structural and suspension system. A poorly distributed load may cause portions of the vehicle to sag, or may induce impermissibly large stresses in the vehicle frame due to the increased bending moments along the vehicle's floor span.
The simplest solution to this problem is to increase the strength of the vehicle frame, but this approach adds weight thereby increasing vehicle fule consumption. If the vehicle body has a cantilevered portion, an uneven load distribution might cause the unsupported area to deflect beyond acceptable limits. The frame reinforcement necessary to prevent such deflection would be quite detrimental to vehicle efficiency due to the increased weight.